Einstein's General Relativity has passed a huge test in the centre of our galaxy

S2 passing supermassive black hole
This artist’s impression shows the path of the star S2 as it passes very close to the supermassive black hole at the centre of the Milky Way. (Credits - Wikimedia Commons)

The theory of General Relativity explained by Albert Einstein in 1915 has yet again been confirmed by another test of a star orbiting our galaxy’s supermassive black hole at insane speed. The study has been published in the Science journal. When the light of a star named S2 approached closest around the black hole, gravitational redshift was observed, stretching out the light by the strong gravitational forces involved.
Last year, a team of researchers announced a similar achievement on S2 or S0-2, one of a group of young, large S-stars orbiting the galactic centre showing clear evidence of gravitational redshift while looping around Sagittarius A*. This new result is from an independent observation set which confirms and elaborates on the first group of results with additional instruments and data for ruling out the biases which might have originated in the tools.
Astronomer Andrea Ghez of the University of California, Los Angeles said that their observations are consistent with Einstein’s theory of general relativity and can definitely rule out Newton’s law of gravity. After 24 years of observation with the sensitive instruments enough to observe the phenomenon in exceptional resolution, it was last year when the star S2 which takes 16 years to orbit Sgr A* was at the closest approach within 17 light-hours of the galactic centre around Sgr A*.
The gravity produced by Sgr A* having a mass equivalent to about 4 million suns is enormous and creates the most extreme condition in the Milky Way. The elliptical path of S2 gets accelerated to stunning speed by this gravity and slingshots around at 25 million kilometres per hour (15.5 million miles per hour) – almost 3 percent of the speed of light. According to relativity, the light of stars should expand into longer wavelengths, towards the red end of the electromagnetic spectrum by the gravitational effect when it comes close to the black hole.
Researchers made spectral observations of the incidents of last year when it reached its maximum velocity in March, followed by closest approach in May, and minimum velocity in September by studying the variations in star’s light as it hurtled around the black hole and finally merging all the spectral observations from 1995 to 2017 to remodel the complete orbit of the star in three dimensions.

Ghez said that study of the motion of stars going through their complete orbit will enable the possibility for the study of General Relativity, fundamental physics and the accurate explanation of the behaviour of a star near a supermassive black hole. These results boost up the outcomes of last year, approving general relativity as strong aspect in understanding the dynamics of gravity.
The test, General relativity has passed in recent times like seeing a three-body star system, an entire galaxy bending space, and the discovery of gravitational waves shows that Einstein’s 100-year-old theory still holds true. Ghez said that at some point we need to shift away from Einstein’s theory because of its vulnerability and develop a universal theory of gravity that completely explains the phenomenon of gravity inside a black hole.
Journal Reference: Science journal


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